PORTLAND, Maine — The two dozen or so liberal activists who had gathered in a darkened cafe on an unusually sticky evening recently were wrestling with a familiar challenge: how to persuade Susan Collins, Maine’s moderate Republican senator, to vote no.

She had already helped sink her party’s effort to repeal the Affordable Care Act, and activists last Tuesday understood that they need to rally the same fervent clamor and rejectionist energy to pressure her to vote no again — this time on the nomination of Judge Brett M. Kavanaugh, President Trump’s Supreme Court nominee.

The problem, so far, isn’t so much with her as with them.

“How do I respond if they are so, so jaded?” asked Susie Crimmins, recounting with frustration her difficulty persuading a pair of neighbors who lobbied Ms. Collins on health care to come back out. “They say she won’t listen.”

The confirmation fight over Judge Kavanaugh was once billed as the mother of all Supreme Court battles, a fight to the death with the court’s ideological balance on the line. Advocacy groups raised seven-figure war chests, warning that Judge Kavanaugh poses an existential threat to abortion rights, the Affordable Care Act and checks on presidential power. Activist ground troops were put on call.

And with Republicans clinging to a single-seat Senate majority, anti-Kavanaugh forces figured they needed just to hold Democrats together in opposition while turning two Republican senators against the nominee — or just one, if Senator John McCain of Arizona remains unavailable for a final vote as he battles brain cancer.

Yet across the country this August, energizing and sustaining on-the-ground opposition to a nominee whom most Republicans and some moderate Democrats have deemed well qualified has been difficult, especially when liberal energy is intensely focused on midterm elections less than 90 days away.

“It’s kind of like, how do we go on? It’s so hard,” Barbara Nelson, a liberal activist from Stanton, Iowa, said after a town-hall meeting in Corning, Iowa, where Senator Charles E. Grassley, chairman of the Senate Judiciary Committee, had met with constituents who were evenly divided over the nomination. “My only hope is that if you just keep saying it often enough, maybe they’ll start believing it.”

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Members of a group called Women for Kavanaugh at a town hall meeting in Corning, Iowa, where Senator Charles E. Grassley spoke.CreditLuke Franke for The New York Times

In Washington, Democrats have struggled to score points against Judge Kavanaugh, a 12-year veteran of the federal bench, pouring considerable energy into a fight with Republicans over access to papers from the years he worked in the White House. Court-focused organizers have found themselves competing with an almost daily barrage of other Trump administration actions, and have struggled to sustain pressure through the summer doldrums.

An advertising blitz without real grass-roots support can go only so far with seasoned politicians.

“I always want to hear from my constituents,” Ms. Collins told reporters on Wednesday after an unrelated event in Orono, Maine. “What is not effective is when these advocacy groups spend millions of dollars on attack ads jamming my phone lines with out-of-state callers.”

Even Washington organizers concede things will need to pick up.

“We have a ways to go in terms of achieving the level of mobilization that we need to see,” said Brian Fallon, the executive director of Demand Justice, a group that promotes progressive judicial nominees, even as he argued that there was a path to defeating Judge Kavanaugh’s nomination.

Mr. Fallon and others are hoping that an August blitz centered on the Senate’s nearly two-week recess can provide a jolt. Larger national advocacy groups — including Planned Parenthood Action Fund and Protect Our Care — told reporters on Monday that they had more than 100 “actions” planned in key states, from letter writing and phone banks to rallies.

In Alaska, voters have been inundated with broadcast and online advertisements targeting Senator Lisa Murkowski, a Republican who, like Ms. Collins, supports abortion rights. And in Nevada, Dean Heller, the most endangered Republican senator up for re-election, has faced a similar barrage.

In Portland, Maine, activists streamed into Ms. Collins’s office each day this past week, sharing with her staff vivid stories of abortions and health crises, iPhone cameras rolling in hand. Signs plastered onto lamp posts and walls around the city asked voters to call Ms. Collins and demand a “no” vote. Labor organizers paused on Thursday during an annual summer teach-in in Orono, not far from Ms. Collins’s home in Bangor, so attendees could call the senator’s office.

“Rise Up for Roe,” a nationwide tour organized by Demand Justice, was scheduled to stop in the city on Sunday.

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Mr. Grassley, the chairman of the Senate Judiciary Committee, said he was surprised that he had not encountered more resistance to Judge Kavanaugh’s nomination.CreditLuke Franke for The New York Times

And in Iowa, activists at the Corning town hall meeting accused Mr. Grassley of “rushing through this confirmation process” from his influential perch atop the Judiciary Committee.

“How do you manage to justify pushing this through, ethically, morally and legally?” asked one woman.

But unlike in 2009, when angry town hall protests helped persuade Mr. Grassley to walk away from bipartisan health care negotiations, the senator this time had plenty of cover to stick to his position on Judge Kavanaugh.

As liberal activists questioned him at the Corning town hall, pro-Kavanaugh activists on a Women for Kavanaugh bus tour were flooding the old opera house where Mr. Grassley was speaking to let him know they had his back.

The National Rifle Association, the Judicial Crisis Network and Americans for Prosperity have matched liberal groups, putting up millions of dollars to target the airwaves and mailboxes of many of the swing states where they believe they can drive a decisive wedge between vulnerable Democratic senators and their party. The Susan B. Anthony List, an anti-abortion group, held recent rallies in Indiana, Missouri and North Dakota, Republican states where Democratic senators are up for re-election.

“It’s premature to consider anyone a lock,” said Brian Walsh, the president of America First Policies, which is working for Judge Kavanaugh’s confirmation. “Until I hear the words ‘I will vote yes,’ nobody is a lock.”

Activity opposing Judge Kavanaugh’s confirmation is more robust than the effort to thwart Neil M. Gorsuch’s confirmation in 2017. But unlike Justice Gorsuch, who replaced a stalwart conservative on the court, Judge Kavanaugh would replace a swing vote in Justice Anthony M. Kennedy and stands poised to tip the ideological balance in key areas.

“Many of these national debates and fights begin with an air of inevitability that the administration will have its way,” said Nan Aron, the president of the liberal Alliance for Justice. “But the Senate has this awesome and active path of deciding whether the nominee is suitable for the court.”

But political realities have quickly set in. Democrats in West Virginia, North Dakota and Indiana — states Mr. Trump won by yawning margins — all supported Justice Gorsuch and are under intense pressure to support Judge Kavanaugh or risk jeopardizing their re-election campaigns.

Ms. Collins insisted she remained undecided and would not make a decision until she had thoroughly reviewed Judge Kavanaugh’s record.

“I think that the rhetoric has been overblown,” she told reporters in Orono.

Groups active here are trying to gently prod Ms. Collins, a voracious reader, to dig into Judge Kavanaugh’s record, and they are trying to flatter her sense of independence. They have collected hundreds of stories from women about abortion and tried to cast the court pick as the latest attack front on the Affordable Care Act.

“Respect is important. We respect her position,” said Nicole Clegg, vice president of public policy at Planned Parenthood of Northern New England. “She has been our senator for more than 20 years.”

Ultimately, though, respect will have to give way to raw political pressure, activists on the ground say.

“If we go into it thinking we are going to change her mind, we have lost it,” Todd Chretien, a veteran activist, said in Maine last week. “We have to go into it thinking we are going to create a political crisis for Collins in which the political cost for her to vote ‘no’ is lower than the political cost to vote ‘yes.’”

Mr. Grassley, for his part, seemed slightly taken aback that he had not met more resistance in his home state.

“If there were any surprises, it would be surprising that every meeting wasn’t like the meeting we just completed,” he said after the event in Corning.

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“I can’t not fight, and I know countless other people who cannot sit back and let this extreme activist judge get appointed without saying we fought every single day,” said Marie Follayttar Smith, the leader of a social justice advocacy group in Maine.CreditTristan Spinski for The New York Times

Activists see no choice but to keep fighting.

“I can’t not fight, and I know countless other people who cannot sit back and let this extreme activist judge get appointed without saying we fought every single day,” said Marie Follayttar Smith, a grass-roots organizer who helped lead the Portland planning meeting. “And while we may understand what D.C. is saying, we can’t stop, and won’t. A lot of people are watching Maine. It is our responsibility.”

A version of this article appears in print on , on Page A14 of the New York edition with the headline: Anti-Kavanaugh Fight Struggles for Traction Among ‘Jaded’ Liberals. Order Reprints | Today’s Paper | Subscribe